Cancel workflow runs which get superseded automatically

.github/workflows/docker.yml

@@ -2,6 +2,9 @@ name: Docker
 on:
   - push
   - pull_request
+concurrency:
+  group: ${{ github.workflow }}-{{ github.head_ref || github.ref }}
+  cancel-in-progress: true
 jobs:
   test:
     name: Docker

.github/workflows/lint.yml

@@ -2,6 +2,9 @@ name: Lint
 on:
   - push
   - pull_request
+concurrency:
+  group: ${{ github.workflow }}-{{ github.head_ref || github.ref }}
+  cancel-in-progress: true
 env:
   os: ubuntu-20.04
   ruby: 2.7

.github/workflows/tests.yml

@@ -2,6 +2,9 @@ name: Tests
 on:
   - push
   - pull_request
+concurrency:
+  group: ${{ github.workflow }}-{{ github.head_ref || github.ref }}
+  cancel-in-progress: true
 jobs:
   test:
     name: Ubuntu ${{ matrix.ubuntu }}, Ruby ${{ matrix.ruby }}